A tandem hexaannulation reaction of benzyllithium involving base-induced cyclodehydrogenation

The reaction of the tribenzo[3.3.3]propellane ketone 1 (triptindan-9-one) with benzyllithium/TMEDA affords an efficient one-pot peri annulation of a dihydronaphthalene across two wings of the propellane framework. The key step of this surprising tandem reaction was determined to be a nucleophilic cyclization of (Z)-9-benzylidenetriptindane (4) with concomitant hydride elimination. The formation of the novel centrotetracyclo[5.5.5.6] framework bearing a distorted (E)-stilbene unit was confirmed by single-crystal X-ray structure analysis.